The pressing demand for petroleous products on the part of industrialized nations has made it necessary to transport considerable quantities of petroleum and its derivatives by sea.
The use of effective means of security, although reducing the risks of environmental pollution, does not however exclude the possibility of accidental dispersions in the sea of more or less vast quantities of petroleous products. These dispersions can be extremely harmful to the environment in that the hydrocarbon substances, which are lighter than water, tend to spread over vast areas, forming a layer on the surface of the water which prevents the exchange of oxygen with the atmosphere, consequently jeopardizing marine life. In addition, the pollution may also effect the coasts causing serious damage both to the ecological equilibrium of the beaches, and to human activities carried out on the coasts (for example harbour traffic and tourism).
The removal of hydrocarbon products dispersed in the water creates numerous difficulties, mainly due to the fact that the most volatile constituents evaporate whereas the heavier fractions tend to form a very viscous and sticky emulsion with the water, which is very difficult to recover with the conventional methods.
To resolve this problem it has been suggested to use absorbent materials which, when put in contact with liquid hydrocarbons, are capable of absorbing them making them easily recuperable.
The main characteristics which make an absorbent material suitable for this type of use are the following:
great affinity with hydrocarbons and consequently high absorbing effect expressed as a quantity of oily substance absorbed per unit by weight of absorbent material; PA1 high surface development of the material to favour contact with the polluting product and consequently improve the absorbing effect; PA1 low specific weight, to guarantee that the material floats on the surface of the water both before and after impregnation with the oily substances; PA1 low degree of stickiness and good consistency of the material once this has absorbed the oily product, to facilitate its recovery; PA1 low cost of absorbent material, to guarantee the economy of the method; PA1 possibility of recycling the material after use to recover both the above material which can therefore be re-used for the same or different purposes, and the absorbed oily product.
Japanese patent JP 48005675 describes the use of a granular mixture containing pellets based on polypropylenic resin, saw-dust and graphite powder, to absorb oily products. After absorption, the above mixture is incinerated.
Japanese patent JP 49030282 discloses a multilayer polypropylene, not interlaced, useful for the removal of oily products.
Japanese patent JP 49053177 describes the use of bags filled with pieces of polypropylene foam (atactic) containing adjoining pores.
Japanese patent JP 57151717 describes absorbing products, which can be used for removing oily products, capable of floating where the floats are placed between sheets of absorbing material. These sheets can be made of synthetic or chemical fibres such as polyolefins, natural fibres, mineral fibres, etc. This patent also indicates the possible use of a combination of products which rapidly absorb and products which slowly absorb oily products such as, for example, polypropylene. In the products described in the known art the absorption of oily products is a consequence of the high surface area of the end-product. Consequently, one of the disadvantages of the products of the known art lies in the fact that the oily products absorbed are easily released from the end-product when it is withdrawn from the contaminated water surface or subjected to light pressure.
Other disadvantages of the methods described in the known art are the impossibility of re-using the products used for the same or different purposes and the low affinity of these with hydrocarbons with a consequently very limited absorbing effect.